In forming an estimate of the civilization and intellectual progress of a newly discovered people, we usually pay attention to their buildings, and other proofs of architectural skill. If we find them, like the wretched inhabitants of Van Diemen's Land, without other abodes than natural caverns or miserable penthouses of bark, we at once regard them as the most ignorant and unhumanized of their race. If, like the natives of the South Sea Isles, they have advanced a step further, and enjoy houses formed of timber, thatched with leaves, and furnished with utensils of different kinds, we are inclined to place them considerably higher in the scale. When, as in the case of ancient Mexico, we discover a nation inhabiting towns containing stone houses, regularly disposed into streets, we do not hesitate without other inquiry to decide that it must have been civilized in no ordinary degree. And if it were to chance that some future Park in Africa should stumble upon the ruins of a large city, where, in addition to these proofs of science, every building was constructed on just geometrical and architectural principles; where the materials were so employed as to unite strength with lightness, and a confined site so artfully occupied as to obtain spacious symmetrical apartments, we should eagerly inquire into the history of the inhabitants, and sigh over the remains of a race whose intellectual advances we should infer with certainty were not inferior to our own.
Were we by the same test to estimate the sagacity of the different classes of animals, we should beyond all doubt assign the highest place to insects, which in the construction of their habitations leave all the rest far behind. The nests of birds, from the rook's rude assemblage of sticks to the pensile dwellings of the tailor-bird, wonderful as they doubtless are, are indisputably eclipsed by the structures formed by many insects; and the regular villages of the beaver, by far the most sagacious architect amongst quadrupeds, must yield the palm to a wasp's nest. You will think me here guilty of exaggeration, and that, blinded by my attachment to a favourite pursuit, I am elevating the little objects, which I wish to recommend to your study, to a rank beyond their just claim. So far, however, am I from being conscious of any such prejudice, that I do not hesitate to go further, and assert that the pyramids of Egypt, as the work of man, are not more wonderful for their size and solidity than are the structures built by some insects.
To describe the most remarkable of these is my present object: and that some method may be observed, I shall in this letter describe the habitations of insects living in a state of solitude, and built each by a single architect; and in a subsequent one, those of insects living in societies, built by the united labours of many. The former class may be conveniently subdivided into habitations built by the parent insect, not for its own use, but for the convenience of its future young; and those which are formed by the insect that inhabits them for its own accommodation. To the first I shall now call your attention.
The solitary insects which construct habitations for their future young without any view to their own accommodation, chiefly belong to the order Hymenoptera, and are principally different species of wild bees. Of these the most simple are built by Colletes[758] succincta, fodiens, &c. The situation which the parent bee chooses, is either the dry earth of a bank, or the vacuities of stone walls cemented with earth instead of mortar. Having excavated a cylinder about two inches in depth, running usually in a horizontal direction, the bee occupies it with three or four cells about half an inch long, and one-sixth broad, shaped like a thimble, the end of one fitting into the mouth of another. The substance of which these cells are formed is two or three layers of a silky membrane, composed of a kind of glue secreted by the animal, resembling gold-beater's leaf, but much finer, and so thin and transparent that the colour of an included object may be seen through them. As soon as one cell is completed, the bee deposits an egg within, and nearly fills it with a paste composed of pollen and honey; which having done, she proceeds to form another cell, storing it in like manner until the whole is finished, when she carefully stops up the mouth of the orifice with earth. Our countryman Grew seems to have found a series of these nests in a singular situation—the middle of the pith of an old elder-branch—in which they were placed lengthwise one after another with a thin boundary between each[759].
Cells composed of a similar membranaceous substance, but placed in a different situation, are constructed by Anthidium manicatum[760]. This gay insect does not excavate holes for their reception, but places them in the cavities of old trees, or of any other object that suits its purpose. Sir Thomas Cullum discovered the nest of one in the inside of the lock of a garden-gate, in which I have also since twice found them. It should seem, however, that such situations would be too cold for the grubs without a coating of some non-conducting substance. The parent bee, therefore, after having constructed the cells, laid an egg in each, and filled them with a store of suitable food, plasters them with a covering of vermiform masses, apparently composed of honey and pollen; and having done this, aware, long before Count Rumford's experiments, what materials conduct heat most slowly, she attacks the woolly leaves of Stachys lanata, Agrostemma coronaria, and similar plants, and with her mandibles industriously scrapes off the wool, which with her fore legs she rolls into a little ball and carries to her nest. This wool she sticks upon the plaster that covers her cells, and thus closely envelops them with a warm coating of down impervious to every change of temperature[761].
The bee last described may be said to exercise the trade of a clothier. Another numerous family would be more properly compared to carpenters, boring with incredible labour out of the solid wood long cylindrical tubes, and dividing them into various cells. Amongst these, one of the most remarkable is Xylocopa[762] violacea, a large species, a native of Southern Europe, distinguished by beautiful wings of a deep violet colour, and found commonly in gardens, in the upright putrescent espaliers or vine-props of which, and occasionally in the garden seats, doors and window-shutters, she makes her nest. In the beginning of spring, after repeated and careful surveys, she fixes upon a piece of wood suitable for her purpose, and with her strong mandibles begins the process of boring. First proceeding obliquely downwards, she soon points her course in a direction parallel with the sides of the wood, and at length with unwearied exertion forms a cylindrical hole or tunnel not less than twelve or fifteen inches long and half an inch broad. Sometimes, where the diameter will admit of it, three or four of these pipes, nearly parallel with each other, are bored in the same piece. Herculean as this task, which is the labour of several days, appears, it is but a small part of what our industrious bee cheerfully undertakes. As yet she has completed but the shell of the destined habitation of her offspring; each of which, to the number of ten or twelve, will require a separate and distinct apartment. How, you will ask, is she to form these? With what materials can she construct the floors and ceilings? Why truly God "doth instruct her to discretion and doth teach her." In excavating her tunnel she has detached a large quantity of fibres, which lie on the ground like a heap of saw-dust. This material supplies all her wants. Having deposited an egg at the bottom of the cylinder along with the requisite store of pollen and honey, she next, at the height of about three quarters of an inch, (which is the depth of each cell,) constructs of particles of the saw-dust glued together, and also to the sides of the tunnel, what may be called an annular stage or scaffolding. When this is sufficiently hardened, its interior edge affords support for a second ring of the same materials, and thus the ceiling is gradually formed of these concentric circles, till there remains only a small orifice in its centre, which is also closed with a circular mass of agglutinated particles of saw-dust. When this partition, which serves as the ceiling of the first cell and the flooring of the second, is finished, it is about the thickness of a crown-piece, and exhibits the appearance of as many concentric circles as the animal has made pauses in her labour. One cell being finished, she proceeds to another, which she furnishes and completes in the same manner, and so on until she has divided her whole tunnel into ten or twelve apartments.
Here, if you have followed me in this detail with the interest which I wish it to inspire, a query will suggest itself. It will strike you that such a laborious undertaking as the constructing and furnishing these cells, cannot be the work of one or even of two days. Considering that every cell requires a store of honey and pollen, not to be collected but with long toil, and that a considerable interval must be spent in agglutinating the floors of each, it will be very obvious to you that the last egg in the last cell must be laid many days after the first. We are certain, therefore, that the first egg will become a grub, and consequently a perfect bee, many days before the last. What then becomes of it? you will ask. It is impossible that it should make its escape through eleven superincumbent cells without destroying the immature tenants; and it seems equally impossible that it should remain patiently in confinement below them until they are all disclosed. This dilemma our heaven-taught architect has provided against. With forethought never enough to be admired she has not constructed her tunnel with one opening only, but at the further end has pierced another orifice, a kind of back-door, through which the insects produced by the first-laid eggs successively emerge into day. In fact, all the young bees, even the uppermost, go out by this road; for, by an exquisite instinct, each grub, when about to become a pupa, places itself in its cell with its head downwards, and thus is necessitated, when arrived at its last state, to pierce its cell in this direction[763].
Ceratina albilabris of Spinola, who has given an interesting account of its manners, forms its cell upon the general plan of the bee just described, but, more economical of labour, chooses a branch of briar or bramble, in the pith of which she excavates a canal about a foot long and one line, or sometimes more, in diameter, with from eight to twelve cells separated from each other by partitions of particles of pith glued together[764].
Such are the curious habitations of the carpenter bees. Next I shall introduce you to the not less interesting structures of another family which carry on the trade of masons, (Megachile muraria,) building their solid houses solely of artificial stone. The first step of the mother bee is to fix upon a proper situation for the future mansion of her offspring. For this she usually selects an angle, sheltered by any projection, on the south side of a stone wall. Her next care is to provide materials for the structure. The chief of these is sand, which she carefully selects grain by grain from such as contains some mixture of earth. These grains she glues together with her viscid saliva into masses the size of small shot, and transports by means of her jaws to the site of her castle[765]. With a number of these masses, which are the artificial stone of which her building is to be composed, united by a cement preferable to ours, she first forms the basis or foundation of the whole. Next she raises the walls of a cell, which is about an inch in length and half an inch broad, and before its orifice is closed in form resembles a thimble. This, after depositing an egg and a supply of honey and pollen, she covers in, and then proceeds to the erection of a second, which she finishes in the same manner, until the whole number, which varies from four to eight, is completed. The vacuities between the cells, which are not placed in any regular order, some being parallel to the wall, others perpendicular to it, and others inclined to it at different angles, this laborious architect fills up with the same material of which the cells are composed, and then bestows upon the whole group a common covering of coarser grains of sand. The form of the whole nest, which when finished is a solid mass of stone so hard as not to be easily penetrated with the blade of a knife, is an irregular oblong of the same colour as the sand, and to a casual observer more resembling a splash of mud than an artificial structure. These bees sometimes are more economical of their labour, and repair old nests, for the possession of which they have very desperate combats. One would have supposed that the inhabitants of a castle so fortified might defy the attacks of every insect marauder. Yet an Ichneumon and a beetle (Clerus apiarius) both contrive to introduce their eggs into the cells, and the larvÆ proceeding from them devour their inhabitants[766].
Other bees of the same family with that last described, use different materials in the construction of their nests. Some employ fine earth made into a kind of mortar with gluten. Another (Osmia[767] cÆrulescens), as we learn from De Geer, forms its nest of argillaceous earth mixed with chalk, upon stone walls, and sometimes probably nidificates in chalk-pits. O. bicornis selects the hollows of large stones for the site of its dwelling; while others prefer the holes in wood.
The works thus far described require in general less genius than labour and patience: but it is far otherwise with the nests of the last tribe of artificers amongst wild bees, to which I shall advert—the hangers of tapestry, or upholsterers—those which line the holes excavated in the earth for the reception of their young, with an elegant coating of flowers or of leaves. Amongst the most interesting of these is Megachile[768] Papaveris, a species whose manners have been admirably described by Reaumur. This little bee, as though fascinated with the colour most attractive to our eyes, invariably chooses for the hangings of her apartments the most brilliant scarlet, selecting for its material the petals of the wild poppy, which she dexterously cuts into the proper form. Her first process is to excavate in some pathway a burrow, cylindrical at the entrance but swelled out below, to the depth of about three inches. Having polished the walls of this little apartment, she next flies to a neighbouring field, cuts out oval portions of the flowers of poppies, seizes them between her legs and returns with them to her cell; and though separated from the wrinkled petal of a half-expanded flower, she knows how to straighten their folds, and, if too large, to fit them for her purpose by cutting off the superfluous parts. Beginning at the bottom, she overlays the walls of her mansion with this brilliant tapestry, extending it also on the surface of the ground round the margin of the orifice. The bottom is rendered warm by three or four coats, and the sides have never less than two. The little upholsterer, having completed the hangings of her apartment, next fills it with pollen and honey to the height of about half an inch; then, after committing an egg to it, she wraps over the poppy lining so that even the roof may be of this material; and lastly closes its mouth with a small hillock of earth[769]. The great depth of the cell compared with the space which the single egg and the accompanying food deposited in it occupy, deserves particular notice. This is not more than half an inch at the bottom, the remaining two inches and a half being subsequently filled with earth.—When you next favour me with a visit, I can show you the cells of this interesting insect as yet unknown to British entomologists, for which I am indebted to the kindness of M. Latreille, who first scientifically described the species[770].
Megachile centuncularis, M. Willughbiella, and other species of the same family, like the preceding, cover the walls of their cells with a coating of leaves, but are content with a more sober colour, generally selecting for their hangings the leaves of trees, especially of the rose, whence they have been known by the name of the leaf-cutter bees. They differ also from M. Papaveris in excavating longer burrows, and filling them with several thimble-shaped cells composed of portions of leaves so curiously convoluted, that, if we were ignorant in what school they have been taught to construct them, we should never credit their being the work of an insect. Their entertaining history, so long ago as 1670, attracted the attention of our countrymen Ray, Lister, Willughby, and Sir Edward King; but we are indebted for the most complete account of their procedures to Reaumur.
The mother bee first excavates a cylindrical hole eight or ten inches long, in a horizontal direction, either in the ground or in the trunk of a rotten willow-tree, or occasionally in other decaying wood. This cavity she fills with six or seven cells wholly composed of portions of leaf, of the shape of a thimble, the convex end of one closely fitting into the open end of another. Her first process is to form the exterior coating, which is composed of three or four pieces of larger dimensions than the rest, and of an oval form. The second coating is formed of portions of equal size, narrow at one end but gradually widening towards the other, where the width equals half the length. One side of these pieces is the serrate margin of the leaf from which it was taken, which, as the pieces are made to lap one over the other, is kept on the outside, and that which has been cut within. The little animal now forms a third coating of similar materials, the middle of which, as the most skilful workman would do in similar circumstances, she places over the margins of those that form the first tube, thus covering and strengthening the junctures. Repeating the same process, she gives a fourth and sometimes a fifth coating to her nest, taking care, at the closed end or narrow extremity of the cell, to bend the leaves so as to form a convex termination. Having thus finished a cell, her next business is to fill it to within half a line of the orifice, with a rose-coloured conserve composed of honey and pollen, usually collected from the flowers of thistles; and then having deposited her egg, she closes the orifice with three pieces of leaf so exactly circular, that a pair of compasses could not define their margin with more truth; and coinciding so precisely with the walls of the cell, as to be retained in their situation merely by the nicety of their adaptation. After this covering is fitted in, there remains still a concavity which receives the convex end of the succeeding cell; and in this manner the indefatigable little animal proceeds until she has completed the six or seven cells which compose her cylinder.
The process which one of these bees employs in cutting the pieces of leaf that compose her nest is worthy of attention. Nothing can be more expeditious: she is not longer about it than we should be with a pair of scissors. After hovering for some moments over a rose-bush, as if to reconnoitre the ground, the bee alights upon the leaf which she has selected, usually taking her station upon its edge so that the margin passes between her legs. With her strong mandibles she cuts without intermission in a curve line so as to detach a triangular portion. When this hangs by the last fibre, lest its weight should carry her to the ground, she balances her little wings for flight, and the very moment it parts from the leaf flies off with it in triumph; the detached portion remaining bent between her legs in a direction perpendicular to her body. Thus without rule or compasses do these diminutive creatures mete out the materials of their work into portions of an ellipse, into ovals or circles, accurately accommodating the dimensions of the several pieces of each figure to each other. What other architect could carry impressed upon the tablet of his memory the entire idea of the edifice which he has to erect, and, destitute of square or plumb-line, cut out his materials in their exact dimensions without making a single mistake? Yet this is what our little bee invariably does. So far are human art and reason excelled by the teaching of the Almighty[771].
Other insects besides bees construct habitations of different kinds for their young, as various species of burrowing wasps (Fossores), Geotrupes, &c., which deposit their eggs in cylindrical excavations that become the abode of the future larvÆ. In the procedures of most of these, nothing worth particularizing occurs; but one species called by Reaumur the mason-wasp, (Odynerus muraria,) referred to in a former letter, works upon so singular a plan, that it would be improper to pass it over in silence, especially as these nests may be found in this country in most sandy banks exposed to the sun. This insect bores a cylindrical cavity from two to three inches deep, in hard sand which its mandibles alone would be scarcely capable of penetrating, were it not provided with a slightly glutinous liquor which it pours out of its mouth, that, like the vinegar with which Hannibal softened the Alps, acts upon the cement of the sand, and renders the separation of the grains easy to the double pickaxe with which our little pioneer is furnished. But the most remarkable circumstance is the mode in which it disposes of the excavated materials. Instead of throwing them at random on a heap, it carefully forms them into little oblong pellets, and arranges them round the entrance of the hole so as to form a tunnel, which, when the excavation is completed, is often not less than two or three inches in length. For the greater part of its height this tunnel is upright, but towards the top it bends into a curve, always however retaining its cylindrical form. The little masses are so attached to each other in this cylinder, as to leave numerous vacuities between them, which give it the appearance of filagree-work. You will readily divine that the excavated hole is intended for the reception of an egg, but for what purpose the external tunnel is meant is not so apparent. One use, and perhaps the most important, would seem to be to prevent the incursions of the artful Ichneumons, ChrysidÆ, &c. which are ever on the watch to insinuate their parasitic young into the nests of other insects: it may render their access to the nest more difficult; they may dread to enter into so long and dark a defile. I have seen, however, more than once a Chrysis come out of these tunnels. That its use is only temporary, is plain from the circumstance that the insect employs the whole fabric, when its egg is laid and store of food procured, in filling up the remaining vacuity of the hole; taking down the pellets, which are very conveniently at hand, and placing them in it until the entrance is filled[772].—Latreille informs us, that a nearly similar tunnel, but composed of grains of earth, is built at the entrance of its cell by a bee of his family of pioneers[773].
Under this head, too, may be most conveniently arranged the very singular habitations of the larvÆ of the LinnÆan genus Cynips, the gall-fly, though they can with no propriety be said to be constructed by the mother, who, provided with an instrument as potent as an enchanter's wand, has but to pierce the site of the foundation, and commodious apartments, as if by magic, spring up and surround the germe of her future descendants. I allude to those vegetable excrescencies termed galls, some of which resembling beautiful berries and others apples, you must have frequently observed on the leaves of the oak, and of which one species, the Aleppo gall, as I have before noticed, is of such importance in the ingenious art "de peindre la parole et de parler aux yeux[774]." All these tumours owe their origin to the deposition of an egg in the substance out of which they grow. This egg, too small almost for perception, the parent insect, a little four-winged fly, introduces into a puncture made by her curious spiral sting, and in a few hours it becomes surrounded with a fleshy chamber, which not only serves its young for shelter and defence, but also for food; the future little hermit feeding upon its interior and there undergoing its metamorphosis. Nothing can be more varied than these habitations. Some are of a globular form, a bright red colour, and smooth fleshy consistence, resembling beautiful fruits, for which indeed, as you have before been told, they are eaten in the Levant: others, beset with spines or clothed with hair, are so much like seed-vessels, that an eminent modern chemist has contended respecting the Aleppo gall, that it is actually a capsule[775]. Some are exactly round; others like little mushrooms; others resemble artichokes; while others again might be taken for flowers: in short, they are of a hundred different forms, and of all sizes from that of a pin's head to that of a walnut. Nor is their situation on the plant less diversified. Some are found upon the leaf itself; others upon the footstalks only; others upon the roots; and others upon the buds[776]. Some of them cause the branches upon which they grow to shoot out into such singular forms, that the plants producing them were esteemed by the old botanists distinct species. Of this kind is the Rose-willow, which old Gerard figures and describes as "not only making a gallant shew, but also yeelding a most cooling aire in the heat of summer, being set up in houses for the decking of the same." This willow is nothing more than one of the common species, whose twigs, in consequence of the deposition of the egg of a Cynips in their summits, there shoot out into numerous leaves totally different in shape from the other leaves of the tree, and arranged not much unlike those composing the flower of a rose, adhering to the stem even after the others fall off. Sir James Smith mentions a similar lusus on the Provence willows, which at first he took for a tufted lichen[777]. From the same cause the twigs of the common wild rose often shoot out into a beautiful tuft of numerous reddish moss-like fibres wholly dissimilar from the leaves of the plant, deemed by the old naturalists a very valuable medical substance, to which they erroneously gave the name of Bedeguar. None of these variations is accidental or common to several of the tribe, but each peculiar to the galls formed by a single and distinct species of Cynips.
How the mere insertion of an egg into the substance of a leaf or twig, even if accompanied, as some imagine, by a peculiar fluid, should cause the growth of such singular protuberances around it, philosophers are as little able to explain, as why the insertion of a particle of variolous matter into a child's arm should cover it with pustules of small pox. In both cases the effects seem to proceed from some action of the foreign substance upon the secreting vessels of the animal or vegetable: but of the nature of this action we know nothing. Thus much is ascertained by the observations of Reaumur and Malpighi—that the production of the gall, which however large attains its full size in a day or two[778], is caused by the egg or some accompanying fluid: not by the larva, which does not appear until the gall is fully formed[779]; that the galls which spring from leaves almost constantly take their origin from nerves[780]; and that the egg, at the same time that it causes the growth of the gall, itself derives nourishment from the substance that surrounds it, becoming considerably larger before it is hatched than it was when first deposited[781].—When chemically analysed, galls are found to contain only the same principles as the plant from which they spring, but in a more concentrated state.
No productions of nature seem to have puzzled the ancient philosophers more than galls. The commentator on Dioscorides, Mathiolus, who agreeably to the doctrine of those days ascribed their origin to spontaneous generation, gravely informs us that weighty prognostications as to the events of the ensuing year may be deduced from ascertaining whether they contain spiders, worms, or flies. Other philosophers, who knew that except by rare accident no other animals are to be found in galls, besides grubs of different kinds which they rationally conceived to spring from eggs, were chiefly at a loss to account for the conveyance of these eggs into the middle of a substance in which they could find no external orifice. They therefore inferred that they were the eggs of insects deposited in the earth, which had been drawn up by the roots of trees along with the sap, and after passing through different vessels had stopped, some in the leaves, others in the twigs, and had there hatched and produced galls! Redi's solution of the difficulty was even more extraordinary. This philosopher, who had so triumphantly combated the absurdities of spontaneous generation, fell himself into greater. Not having been able to witness the deposition of eggs by the parent flies in the plants that produce galls, he took it for granted that the grubs which he found within them could not spring from eggs: and he was equally unwilling to admit their origin from spontaneous generation,—an admission which would have been fatal to his own most brilliant discoveries. He therefore cut the knot, by supposing that to the same vegetative soul by which fruits and plants are produced, is committed the charge of creating the larvÆ found in galls[782]! An instance truly humiliating, how little we can infer from a man's just ideas on one point, that he will not be guilty of the most pitiable absurdity on another!
Though by far the greater part of the vegetable excrescencies termed galls, are caused by insects of the genus Cynips, they do not always originate from this tribe. Some are produced by weevils belonging to SchÜppel's genus Ceutorhynchus; as those on the roots of kedlock (Sinapis arvensis), which I have ascertained to be inhabited by the larvÆ of Curculio contractus Marsh., RhynchÆnus assimilis, F. From the knob-like galls on turnips called in some places the anbury, I have bred another of these weevils, (Curculio pleurostigma, Marsh., RhynchÆnus sulcicollis, Gyll.) and I have little doubt that the same insects, or species allied to them, cause the clubbing of the roots of cabbages. It seems to be a beetle of the same family that is figured by Reaumur[783], as causing the galls on the leaves of the lime-tree. Others owe their origin to moths, as those resembling a nutmeg which Reaumur received from Cyprus[784]; and others again to two-winged flies, as the woody galls of the thistle caused by Trypeta Cardui[785], and the cottony galls found on ground ivy, wild thyme, &c. as well as a very singular one on the juniper resembling a flower, described by De Geer[786], all which are the work of minute gall-gnats (CecidomyiÆ, Latr.). Some of these last convert even the flowers of plants into a kind of galls, as T. Loti of De Geer[787], which inhabits the blossoms of Lotus corniculatus; and one which I have myself observed to render the flowers of Erysimum Barbarea like a hop blossom. A similar monstrous appearance is communicated to the flowers of Teucrium supinum by a little field-bug, Tingis Teucrii of Host[788], and to another plant of the same genus by one of the same tribe described by Reaumur[789]. In these two last instances, however, the habitations do not seem strictly entitled to the appellation of galls, as they originate not from the egg, but from the larva, which, in the operation of extracting the sap, in some way imparts a morbid action to the juices, causing the flower to expand unnaturally: and the same remark is applicable to the gall-like swellings formed by many Aphides, as A. PistaciÆ, which causes the leaves of different species of Pistacia to expand into red finger-like cavities; A. Abietis, which converts the buds or young shoots of the fir into a very beautiful gall, somewhat resembling a fir-cone, or a pine-apple in miniature; and A. BursariÆ, which with its brood inhabits angular utriculi on the leafstalk of the black poplar, numbers of which I have observed on those trees by the road-side from Hull to Cottingham.—The majority of galls are what entomologists have denominated monothalamous, or consisting of only one chamber or cell; but some are polythalamous, or consisting of several.
Having thus described the most remarkable of the habitations constructed by the parent insects for the accommodation of their future young, I proceed to the second kind mentioned, namely, those which are formed by the insect itself for its own use. These may be again subdivided into such as are the work of the insects in their larva state; and such as are formed by perfect insects.
Many larvÆ of all orders need no other habitations than the holes which they form in seeking for, or eating, the substances upon which they feed. Of this description are the majority of subterranean larvÆ, and those which feed on wood, as the Bostrichi or labyrinth beetles; the Anobia which excavate the little circular holes frequently met with in ancient furniture and the wood work of old houses; and many larvÆ of other orders, particularly Lepidoptera. One of these last, the larva of Cossus ligniperda differs from its congeners in fabricating for its residence during winter a habitation of pieces of wood lined with fine silk[790]. Under this division, too, come the singular habitations of the subcutaneous larvÆ, so called from the circumstance of their feeding upon the parenchyma included between the upper and under cuticles of the leaves of plants, between which, though the whole leaf is often not thicker than a sheet of writing-paper, they find at once food and lodging. You must have been at some time struck by certain white zigzag or labyrinth-like lines on the leaves of the dandelion, bramble, and numerous other plants: the next-time you meet with one of them, if you hold it up to the light you will perceive that the colour of these lines is owing to the pulpy substance of the leaf having there been removed; and at the further end you will probably remark a dark-coloured speck, which, when carefully extricated from its covering, you will find to be the little miner of the tortuous galleries which you are admiring. Some of these minute larvÆ, to which the parenchyma of a leaf is a vast country, requiring several weeks to be traversed by the slow process of mining which they adopt—that of eating the excavated materials as they proceed—are transformed into beetles (Cionus Thapsi, &c.); others into flies; and a still greater number into very minute moths, as Gracillaria? Wilkella, Clerkella, &c. Many of these last are little miracles of nature, which has lavished on them the most splendid tints tastefully combined with gold, silver and pearl: so that, were they but formed upon a larger scale, they would far eclipse all other animals in richness of decoration.
Another tribe of larvÆ, not very numerous, content themselves for their habitations with simple holes, into which they retire occasionally. Many of these are merely cylindrical burrows in the ground, as those formed by the larvÆ of field-crickets, CicindelÆ and EphemerÆ. But the larvÆ of the very remarkable lepidopterous genus (Nycterobius of Mr. MacLeay) before alluded to[791], excavate for themselves dwellings of a more artificial construction; forming cylindrical holes in the trees of New Holland, particularly the different species of Banksia, to which they are very destructive, and defending the entrance against the attacks of the Mantes and other carnivorous insects by a sort of trap-door composed of silk interwoven with leaves and pieces of excrement, securely fastened at the upper end, but left loose at the lower for the free passage of the occupant. This abode they regularly quit at sun-set, for the purpose of laying in a store of the leaves on which they feed. These they drag by one at a time into their cell until the approach of light, when they retreat precipitately into it, and there remain closely secluded the whole day, enjoying the booty which their nocturnal range has provided. One species lifts up the loose end of its door by its tail, and enters backward, dragging after it a leaf of Banksia serrata, which it holds by the footstalk[792].
A third description of larvÆ, chiefly of the two lepidopterous tribes TortricidÆ and TineidÆ, form into convenient habitations the leaves of the plants on which they feed. Some of these merely connect together with a few silken threads several leaves so as to form an irregular packet, in the centre of which the little hermit lives. Others confine themselves to a single leaf, of which they simply fold one part over the other. A third description form and inhabit a sort of roll, by some species made cylindrical, by others conical, resembling the papers into which grocers put their sugar, and as accurately constructed, only there is an opening left at the smaller extremity for the egress of the insect in case of need. If you were to see one of these rolls, you would immediately ask by what mechanism it could possibly be made—how an insect without fingers could contrive to bend a leaf into a roll, and to keep it in that form until fastened with the silk which holds it together? The following is the operation. The little caterpillar first fixes a series of silken cables from one side of the leaf to the other. She next pulls at these cables with her feet; and when she has forced the sides to approach, she fastens them together with shorter threads of silk. If the insect finds that one of the larger nerves of the leaf is so strong as to resist her efforts, she weakens it by gnawing it here and there half through. What engineer could act more sagaciously?—To form one of the conical or horn-shaped rolls, which are not composed of a whole leaf, but of a long triangular portion cut out of the edge, some other manoeuvres are requisite. Placing herself upon the leaf, the caterpillar cuts out with her jaws the piece which is to compose her roll. She does not however entirely detach it: it would then want a base. She detaches that part only which is to form the contour of the horn. This portion is a triangular strap, which she rolls as she cuts. When the body of the horn is finished, as it is intended to be fixed upon the leaf in nearly an upright position, it is necessary to elevate it. To effect this, she proceeds as we should with an inclined obelisk. She attaches threads or little cables towards the point of the pyramid, and raises it by the weight of her body[793].
A still greater degree of dexterity is manifested in fabricating the habitations of the larvÆ of some other moths which feed on the leaves of the rose-tree, apple, elm, and oak, on the under-side of which they may in summer be often found. These form an oblong cavity in the interior of a leaf by eating the parenchyma between the two membranes composing its upper and under side, which, after having detached them from the surrounding portion, it joins with silk so artfully that the seams are scarcely discoverable even with a lens, so as to compose a case or horn, cylindrical in the middle, its anterior orifice circular, its posterior triangular. Were this dwelling cylindrical in every part, the form of the two pieces that compose it would be very simple; but the different shape of the two ends renders it necessary that each side should have peculiar and dissimilar curvatures; and Reaumur assures us, that these are as complex and difficult to imitate as the contours of the pieces of cloth that compose the back of a coat. Some of this tribe, whose proceedings I had the pleasure of witnessing a short time since upon the alders in the Hull Botanic Garden, more ingenious than their brethren, and willing to save the labour of sewing up two seams in their dwelling, insinuate themselves near the edge of a leaf instead of in its middle. Here they form their excavation, mining into the very crenatures between the two surfaces of the leaf, which, being joined together at the edge, there form one seam of the case, and from their dentated figure give it a very singular appearance, not unlike that of some fishes which have fins upon their backs. The opposite side they are necessarily forced to cut and sew up, but even in this operation they show an ingenuity and contrivance worthy of admiration. The moths, which cut out their suit from the middle of the leaf, wholly detach the two surfaces that compose it before they proceed to join them together, the serrated incisions made by their teeth, which, if they do not cut as fast, in this respect are more effective than any scissors, interlacing each other so as to support the separated portions until they are properly joined. But it is obvious that this process cannot be followed by those moths which cut out their house from the edge of a leaf. If these were to detach the inner side before they had joined the two pieces together, the builder as well as his dwelling would inevitably fall. They therefore, before making any incision, prudently run (as a sempstress would call it) loosely together in distant points the two membranes on that side. Then putting out their heads they cut the intermediate portions, carefully avoiding the larger nerves of the leaf; afterwards they sew up the detached sides more closely, and only intersect the nerves when their labour is completed[794].—The habitation made by a moth, which lives upon a species of Astragalus, is in like manner formed of the epidermis of the leaves, but in this several corrugated pieces project over each other, so as to resemble the furbelows once in fashion[795].
Other larvÆ construct their habitations wholly of silk. Of this description is that of a moth, whose abode, except as to the materials which compose it, is formed on the same general plan as that just described, and the larva in like manner feeds only on the parenchyma of the leaf. In the beginning of spring, if you examine the leaves of your pear-trees, you will scarcely fail to meet with some beset on the under surface with several perpendicular downy russet-coloured projections, about a quarter of an inch high, and not much thicker than a pin, of a cylindrical shape, with a protuberance at the base, and altogether resembling at first sight so many spines growing out of the leaf. You would never suspect that these could be the habitations of insects; yet that they are is certain. Detach one of them, and give it a gentle squeeze, and you will see emerge from the lower end a minute caterpillar with a yellowish body and black head. Examine the place from which you have removed it, and you will perceive a round excavation in the cuticle and parenchyma of the leaf, the size of the end of the tube by which it was concealed. This excavation is the work of the above-mentioned caterpillar, which obtains its food by moving its little tent from one part of the leaf to the other, and eating away the space immediately under it. It touches no other part; and when these insects abound, as they often do to the great injury of pear-trees[796], you will perceive every leaf bristled with them, and covered with little withered specks, the vestiges of their former meals. The case in which the caterpillar resides, and which is quite essential to its existence, is composed of silk spun from its mouth almost as soon as it is excluded from the egg. As it increases in size, it enlarges its habitation by slitting it in two, and introducing a strip of new materials. But the most curious circumstance in the history of this little Arab is the mode by which it retains its tent in a perpendicular posture. This it effects partly by attaching silken threads from the protuberance at the base to the surrounding surface of the leaf. But being not merely a mechanician, but a profound natural philosopher well acquainted with the properties of air, it has another resource when any extraordinary violence threatens to overturn its slender turret. It forms a vacuum in the protuberance at the base, and thus as effectually fastens it to the leaf as if an air-pump had been employed! This vacuum is caused by the insect's retreating on the least alarm up its narrow case, which its body completely fills, and thus leaving the space below free of air. In detaching one of these cases you may easily convince yourself of the fact. If you seize it suddenly while the insect is at the bottom, you will find that it is readily pulled off, the silken cords giving way to a very slight force; but if, proceeding gently, you give the insect time to retreat, the case will be held so closely to the leaf as to require a much stronger effort to loosen it. As if aware that, should the air get admission from below, and thus render a vacuum impracticable, the strongest bulwark of its fortress would be destroyed, our little philosopher carefully avoids gnawing a hole in the leaf, contenting itself with the pasturage afforded by the parenchyma above the lower epidermis; and when the produce of this area is consumed, it gnaws asunder the cords of its tent, and pitches it at a short distance as before. Having attained its full growth, it assumes the pupa state, and after a while issues out of its confinement a small brown moth, with long hind legs, the PhalÆna Tinea serratella of LinnÉ[797].
Some larvÆ, which form their covering of pure silk, are not content with a single coating, but actually envelop themselves in another, open on one side and very much resembling a cloak; whence Reaumur called them "Teignes À fourreau À manteau." What is very striking in the construction of this cloak, is, that the silk, instead of being woven into one uniform close texture, is formed into numerous transparent scales over-wrapping each other, and altogether very much resembling the scales of a fish[798]. These mantle-covered cases, one of which I once had the pleasure of discovering, are inhabited by the larva of a little moth apparently first described by Dr. Zincken genannt Sommer, who calls it Tinea palliatella[799].
Various substances besides silk are fabricated into habitations by other larvÆ, though usually joined together either with silk or an analogous gummy material. Thus Diurnea? Lichenum forms of pieces of lichen a dwelling resembling one of the turreted Helices, many of which I observed in June 1812 on an oak in Barham. The larvÆ of another moth, which also feeds upon lichens, instead of employing these vegetables in forming its habitation, composes it of grains of stone eroded from the walls of buildings upon which its food is found, and connected by a silken cement. These insects were the subject of a paper in the Memoirs of the French Academy[800], by M. de la Voye, who, from the circumstance of their being found in great abundance on mouldering walls, attributed to them the power of eating stone, and regarded them as the authors of injuries proceeding solely from the hand of time: for the insects themselves are so minute, and the coating of grains of stone composing their cases is so trifling, that Reaumur observes they could scarcely make any perceptible impression on a wall from which they had procured materials for ages[801].—Another lepidopterous larva, but of a much larger size and different genus, the case of which is preserved in the cabinet of the President of the Linnean Society, who pointed it out to me, employs the spines apparently of some species of Mimosa, which are ranged side by side so as to form a very elegant fluted cylinder. A similar arrangement of pieces of small twigs is observable in the habitation of the females[802] of the larvÆ of a moth referred by Von Scheven to Bombyx vestita, F.; which Ochsenheimer regards as synonymous with Psyche graminella, while P. Viciella of the Wiener Verzeichniss covers itself with short portions of the stems of grasses placed transversely, and united by means of silk into a five- or six-sided case. The habitation of a third larva of the same family, described and figured by Reaumur (P. graminella, Ochsenh. just named), is composed of squarish pieces of the leaves of grass fastened only at one end, and overwrapping each other like the tiles of a house; and that of another noticed by the same author, of portions of the smallest twigs of broom arranged on the same plan[803]. Indeed the larvÆ of the whole of this tribe of moths, now separated into a distinct genus (Psyche, Schrank, Ochsenh., Fumea, Haworth), but which according to Germar needs further subdivision, reside in cases or sacks (whence they are called by the Germans SacktrÄger) composed of silk, and fragments of grass, bark, &c.
The larvÆ of a small beetle (Clytra longimana) reside in oviform cases apparently of a calcareous or earthy substance, joined by a gummy cement and covered with red hairs, the origin of which, HÜbner, who first discovered them, could not account for: and from the observations of Amstein and the French translator of Fuessly's Archives, it seems probable that the larvÆ of all the species of Clytra, and according to Zschorn, at least of one species of Cryptocephalus, (C. duodecimpunctatus) differing in this respect from all other known Coleoptera, live in moveable cases[804]. I have however found a species of Limnius (L. Æneus) inhabiting a fixed case made of particles of stone or sand.
Wax is the principal substance employed in the habitations of the larvÆ before mentioned[805], occasionally so destructive to bee-hives. These insidious depredators, which are mentioned by Aristotle[806], tying together, with silk, grains of wax (which, and not honey, forms their food), construct galleries of a considerable length, and thus concealed from the sight, and protected from the stings of the armed people whom they have attacked, push their mines into the very heart of the fortress, and pursue their robberies in perfect safety[807].
As many of the habitations which I have been describing, fit the body of the insects as close as a coat, they might perhaps with more propriety be called clothes. This is certainly the most appropriate designation of the abodes of some species of TineÆ (the clothes' moths), which not only cover themselves with a coat, but employ the very same material in its composition as we do in ours, forming it of wool or hair curiously felted together. Like us, they are born naked, but not like us helpless at that period, scarcely have they breathed before they begin to clothe themselves; thus contradicting Dr. Paley's assertion, that "the human animal is the only one which is naked, and the only one which can clothe itself[808]:" and wisely inattentive to change of fashion, the same suit serves them from their birth to mature age. The shape of their dress is adapted to that of their body—a cylindrical case open at both ends. The stuff of which it is composed is the manufacture of the larva of the moth (Tinea), which incorporates wool or hair artfully cut from our clothes or furniture, with silk drawn from its own mouth, into a warm and thick tissue: and as this would not be soft enough for its tender skin, it also lines the inside of its coat with a layer of pure silk. Since this suit of clothes during the earliest age of the insect accurately fits its body, you will readily conceive that it will frequently require enlarging. This the little occupant accomplishes as dexterously as any tailor. If the case merely requires lengthening, the task is easy. All that is needful is to add a new ring of hair or wool and silk to each end. But to enlarge it in width is not so simple an affair. Yet it sets to work precisely as we should, slitting the case on the two opposite sides, and then adroitly inserting between them two pieces of the requisite size. It does not, however, cut open the case from one end to the other at once: the sides would separate too far asunder, and the insect be left naked. It therefore first cuts each side about half way down, and then after having filled up the fissure proceeds to cut the remaining half: so that, in fact, four enlargements are made, and four separate pieces inserted.—The colour of the habit is always the same as that of the stuff from which it is taken. Thus, if its original colour be blue, and the insect previously to enlarging it be put upon red cloth, the circles at the end and two stripes down the middle will be red. If placed alternately upon cloths of different hues, its dress will be parti-coloured like that of a Harlequin.—The injury occasioned to us by these insects is not confined to the quantity of materials consumed in clothing and feeding themselves. In moving from place to place they seem to be as much incommoded by the long hairs which surround them, as we are by walking amongst high grass; and accordingly, marching scythe in hand, with their teeth they cut out a smooth road, from time to time reposing themselves, and anchoring their little case with small silken cables.
If, as I hope, you are induced to investigate the manners of these insects, you have but to leave an old coat for a few months undisturbed in a dark closet, and you may be pretty certain of meeting with an abundant colony.
Not merely wool or hair, but another substance analogous to one employed in our dress, is adopted for their clothing by other insects. The larva of a fly which lives on the seeds of willows, makes itself a very beautiful case of their cottony down, not only impervious to wet and cold, but serving, if accidentally blown into the water, which from the situation of these trees frequently happens, as a buoyant little barge which is wafted safely to the shore[809].
The habitations which we have hitherto been considering, are formed by larvÆ that live on land, but others equally remarkable are constructed by aquatic species, the larvÆ of the various PhryganeÆ L., a tribe of four-winged insects which an ordinary observer would call moths, but which are even of a distinct order (Trichoptera), not having their wings covered by the scales which adorn the lepidopterous race. If you are desirous of examining the insects to which I am alluding, you have only to place yourself by the side of a clear and shallow pool of water, and you cannot fail to observe at the bottom little oblong moving masses resembling pieces of straw, wood, or even stone. These are the larvÆ in question, well known to fishermen by the title of Caddis-worms, and which, if you take them out of the water, you will observe to inhabit cases of a very singular conformation. Of the larva itself, which somewhat resembles the caterpillars of many Lepidoptera, nothing is to be seen but the head and six legs by means of which it moves itself in the water, and drags after it the case in which the rest of the body is inclosed, and into which on any alarm it wholly retires. The construction of these habitations is very various. Some select four or five pieces of the leaves of grass, which they glue together into a shapely polygonal case; others employ portions of the stems of rushes, placed side by side so as to form an elegant fluted cylinder; some arrange round them pieces of leaves like a spirally-rolled ribband[810]; others inclose themselves in a mass of the leaves of any aquatic plants united without regularity; and others again form their abode of minute pieces of wood either fresh or decayed[811]. One, like the SabellÆ[812], forms a horn-shaped case composed of grains of sand, so equal in size, and so nicely and regularly gummed together, the sides throughout being of the thickness of one grain only, that the first time I viewed it I could scarcely persuade myself it could be the work of an insect. The case of Leptocerus bimaculatus, which is less artificially constructed of a mixture of mud and sand, is pyriform, and has its end curiously stopped by a plate formed of grains of sand, with a central aperture[813]. Other species construct houses which may be called alive, forming them of the shells of various aquatic snails of different kinds and sizes even while inhabited, all of which are immoveably fixed to it, and dragged about at its pleasure—a covering as singular as if a savage, instead of clothing himself with squirrels' skins, should sew together into a coat the animals themselves. However various may be the form of the case externally, within it is usually cylindrical and lined with silk; and though seldom apparently wider than just to admit the body of the insect, some species have the power of turning round in it, and of putting out their head at either end[814]. Some larvÆ constantly make their cases of the same materials; others employ indifferently any that are at hand; and the new ones which they construct as they increase in size (for they have not the faculty, like the larva of the moth, of enlarging them) have often an appearance quite dissimilar to that of the old. Even those that are most careless about the nature of the materials of their house, are solicitously attentive to one circumstance respecting them, namely, their specific gravity. Not having the power of swimming, but only of walking at the bottom of the water by aid of the six legs attached to the fore part of the body which is usually protruded out of the case, and the insect itself being heavier than water, it is of great importance that its house should be of a specific gravity so nearly that of the element in which it resides, as while walking neither to incommode it by its weight, nor by too great buoyancy; and it is as essential that it should be so equally ballasted in every part as to be readily moveable in any position. Under these circumstances our Caddis-worms evince their proficiency in hydrostatics, selecting the most suitable substances; and, if the cell be too heavy, glueing to it a bit of leaf or straw; or, if too light, a shell or piece of gravel. It is from this necessity of regulating the specific gravity, that to the cases formed with the greatest regularity we often see attached a seemingly superfluous piece of wood, leaf, or the like.
A larva of one of the aquatic TipulariÆ lives in cases somewhat similar to those of some PhryganeÆ. Several of these of a fusiform shape and brown colour, composed partly of silk and partly perhaps of fragments of leaves, and inhabited by a red larva apparently of a Chironomus, were found by Reaumur upon dead leaves in a pool of water in the Bois de Boulogne[815].
In concluding this head I may observe, that here might have been described the various abodes which solitary larvÆ prepare for themselves previously to assuming the pupa, and intended for their protection in that defenceless stage of existence; but as I shall have occasion again to refer to them in speaking of the larva state of insects, I shall defer their description to that letter, to which they more strictly belong.
From the next division of the habitations of insects—those formed by solitary perfect insects for their own accommodation—I shall select for description only two, both the work of spiders, and alluded to in a former letter, which indeed, with the exception of the inartificial retreats made by the Grylli, CicindelÆ, and perhaps a few others, are the only ones properly belonging to it.
The habitation of one of these (Cteniza cÆmentaria) is subterraneous, not a mere shallow cavity, but a tube or gallery upwards of two feet in length and half an inch broad. This tunnel, so vast compared with the size of the insect, it digs by means of its strong jaws in a steep bank of bare clay, so that the rain may readily run off without penetrating to its dwelling. Its next operation is to line the whole from top to bottom with a web of fine silk, which serves the double purpose of preventing the earth that composes the walls from falling in, and, by its connexion with the door of the orifice, of giving information to the spider of what is passing above. You doubtless suppose that in saying door I am speaking metaphorically. It could never enter into your conception that any animal, much less an insect, could construct any thing really deserving of that name—any thing like our doors, turning upon a hinge, and accurately fitted to the frame of the opening which it is intended to close. Yet such a door, incredible as it may seem, is actually framed by this spider. It does not indeed, like us, compose it of wood, but of several coats of dried earth fastened to each other with silk. When finished, its outline is as perfectly circular as if traced with compasses; the inferior surface is convex and smooth, the superior flat and rough, and so like the adjoining earth as not to be distinguishable from it. This door the ingenious artist fixes to the entrance of her gallery by a hinge of silk, which plays with the greatest freedom, and allows it to be opened and shut with ease; and as if acquainted with the laws of gravity, she invariably fixes the hinge at the highest side of the opening, so that the door when pushed up shuts again by its own weight. She has not less sagaciously left a little edge or groove just within the entrance, upon which the door closes, and to which it fits with such precision, that it seems to make but one surface with it. Such is the astonishing structure of this little animal's abode; nor is its defence of its subterraneous cavern less surprising. If an observer adroitly insinuates the point of a pin under the edge of the door, and elevates it a little, he immediately perceives a very strong resistance.—What is its cause?—The spider, warned by the vibrations of the threads which extend from the door to the bottom of her gallery, runs with all speed to the door, fastens its legs to it on one side, and on the other to the walls, and, turning upon its back, pulls with all its might. Thus the door is alternately shut or opened, as the exertions of the observer or of the spider prevail. It is easy to guess which will in the end conquer; and the spider, when it finds all resistance ineffectual, betakes itself to flight, and retreats. If, to make a further experiment, the observer fastens down the door so that it cannot be forced open, the next morning he will find a new entrance, with a new door formed at a small distance; or, if he take the door entirely away, another will be constructed in less than twelve hours.
The habitation thus singularly formed and defended is not at all used as a snare, but merely as a safe abode for the spider, which hunts its prey at night only; and, when caught, devours it in security at the bottom of its den, which is generally strewed with the remains of coleopterous insects[816].—From some curious observations of M. Dorthes on this species in the second volume of the Linnean Transactions, it appears that both the male and female spider and as many as thirty young ones occasionally inhabit one of these galleries.—Mygale Sauvagesii of Rossi, which is a distinct species found in Corsica, forms a similar habitation[817].
The galleries just described are the work of an European species not uncommon in the south of France; but similar ones are fabricated by Thomisus venatorius, an inhabitant of the West India islands, as well as by many other tropical species. I have seen one of these, which had been dug out of the earth, in the cabinet of Thomas Hall, Esq. F.L.S., that was nearly a foot in length, and above an inch in diameter, forming a cylindrical bag of dark-coloured silk, closed at the bottom, and accurately fitted at the top by a door or lid.
The habitation of Argyroneta aquatica, the other spider to which I alluded, is chiefly remarkable for the element in which it is constructed and the materials that compose it. It is built in the midst of water, and formed, in fact, of air! Spiders are usually terrestrial, but this is aquatic, or rather amphibious; for though she resides in the midst of water, in which she swims with great celerity, sometimes on her belly but more frequently on her back, and is an admirable diver, she not unfrequently hunts on shore, and, having caught her prey, plunges with it to the bottom of the water. Here it is she forms her singular and unique abode. She would evidently have but a very uncomfortable time were she constantly wet, but this she is sagacious enough to avoid; and by availing herself of some well-known philosophical principles, she constructs for herself an apartment in which, like the mermaids and sea-nymphs of fable, she resides in comfort and security. The following is her process. First she spins loose threads in various directions attached to the leaves of aquatic plants, which may be called the frame-work of her chamber, and over them she spreads a transparent varnish resembling liquid glass, which issues from the middle of her spinners, and which is so elastic that it is capable of great expansion and contraction: and if a hole be made in it, it immediately closes again. Next she spreads over her belly a pellicle of the same material, and ascends to the surface. The precise mode in which she transfers a bubble of air beneath this pellicle is not accurately known; but from an observation made by the ingenious author of the little work from which this account is abstracted, he concludes that she draws the air into her body by the anus, which she presents to the surface of the pool, and then pumps it out from an opening at the base of the belly between the pellicle and that part of the body, the hairs of which keep it extended. Clothed with this aËrial mantle, which to the spectator seems formed of resplendent quicksilver, she plunges to the bottom, and, with as much dexterity as a chemist transfers gas with a gas-holder, introduces her bubble of air beneath the roof prepared for its reception. This manoeuvre she repeats ten or twelve times, until at length in about a quarter of an hour she has transported as much air as suffices to expand her apartment to its intended extent, and now finds herself in possession of a little aËrial edifice, I had almost said an enchanted palace, affording her a commodious and dry retreat in the very midst of the water. Here she reposes unmoved by the storms that agitate the surface of the pool, and devours her prey at ease and in safety. Both sexes form these lodgings. At a particular season of the year the male quits his apartment, approaches that of the female, enters it, and enlarging it by the bubble of air that he carries with him, it becomes a common abode for the happy pair[818].—The spider which forms these singular habitations is one of the largest European species, and in some countries not uncommon in stagnant pools.
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